Table of Contents
What is circulate units?
Continuity of circulate equation
Common flow unit metering strategies in open channels
Eyeball method
Flow depth (Manning)
Main equipment
Surface Velocity Meters
Transport time meters
Flow unit measurement strategies in full tube purposes
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is flow units?
Flow rate is the amount of fluid that passes by way of a unit of time. In water resources, flow is usually measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite so much of different models. The measurement of water useful resource flow is essential for functions corresponding to system control, billing, design and lots of other functions. There are a number of ways to measure move in a water resource system. This article outlines a few of the extra common methods of circulate measurement and provides some helpful details about move models measurement.
Continuity of circulate equation
For water flowing in a pipe underneath steady-state circumstances (i.e., not various with time), continuity implies that water flowing into one finish of the pipe must circulate out of the opposite end. This additionally implies that the circulate within the pipe is similar at any point along the size of the pipe. The continuity equation may be expressed as
Flow = Velocity * Area
The concept of continuity in steady state conditions ends in the product of velocity * area being equal to a continuing at any point in the pipe. This is a useful principle for making flow measurements, as proven beneath.
This is an instance of utilizing the continuity equation to calculate move. Velocity is measured at 10 feet per second and the cross-sectional space of the circulate is measured at 10 sq. ft. Flow price = 10 toes per second * 10 sq. toes = one hundred cubic ft per second.
Common flow unit metering methods in open channels
Eyeball methodology
It is usually helpful to estimate the move velocity and cross-sectional space by eye and then multiply the flow velocity by the area to obtain the circulate velocity (continuity equation). A ruler or tape measure can be used to enhance the accuracy of cross-sectional area measurements, and a stopwatch can be used to improve velocity measurements by timing floating particles transferring a set distance. The eyeball methodology can be used to estimate circulate when only an “order of magnitude” of move is required or when the circulate price is too low to be measured with a move meter.
Flow depth (Manning)
When the channel cross-sectional area and channel slope are known and uniform move circumstances exist, the Manning’s equation can be used to calculate circulate by measuring depth solely. The Manning’s equation is an empirical equation that describes the connection between flow rate in an open channel underneath uniform move situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate means that depth doesn’t range with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth are not relevant to steadily altering circulate circumstances, similar to backwater circumstances upstream of a dam or weir.
The depth flow methodology of flow measurement is more accurate than the “eyeball” method. The major challenge with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform circulate circumstances. This technique is often used with ultrasonic flow meters to estimate the flow of a river by measuring solely the water level of the river. Often in these causes, the river level/flow relationship is developed with the help of advanced river hydraulic models to account for complex channel geometry and channel friction circumstances.
Main equipment
The main system is used to measure move in open channels, using buildings corresponding to flumes, weirs or dams, to measure move by measuring depth. The measured depth can then be converted to a move rate utilizing an equation or rated curve equation.
Primary devices work by forcing the flow by way of a path of crucial depth, for example on the high of a weir or on the throat of a flume. In technical phrases, the crucial depth is outlined as the depth of the minimal specific energy state that ends in a specific discharge. In ไดอะแฟรม , this minimum state of vitality implies that only one circulate corresponds to the crucial depth. Therefore, measuring solely the depth produces a measurement of the corresponding flux and is due to this fact called a “primary” device.
Primary gadgets are a really handy methodology of circulate measurement as a result of the depth could be measured from above the flow with out the want to insert a sensor within the water. This makes primary move meters extra dependable and easier to take care of. A drawback of main gadgets is that they’ll trigger head loss and backwater within the system. Primary units are sometimes considered to be essentially the most correct technique of measuring open channel circulate.
Surface Velocity Meters
An area velocity meter is an open channel flow meter that measures circulate by making two separate measurements of depth and velocity. The depth is converted to a cross-sectional space utilizing the geometry of the pipe or channel. The flow fee is then calculated by multiplying the circulate area by the speed utilizing the continuity equation, therefore the title “AV meter”. Velocity is often measured utilizing a Doppler sensor, which reflects ultrasound waves back from particles within the fluid and uses the Doppler shift in the mirrored sound signal to estimate velocity. Some AV meters measure surface velocity optically to estimate velocity.
AV meters are sometimes used to measure open channel move in sewers because the probes are comparatively small and they can be put in in existing sewer pipes with out inflicting important head loss in the pipe. This additionally allows them for use for momentary or short-term flow metering functions for sewer research. one disadvantage of AV meters is that the sensor should be installed in the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are often thought-about less accurate than primary move meters as a result of major gadgets solely have to measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters
Transport time meters have been developed within the oil trade to accurately measure move in large pipelines. They have been used with some success for open channel flow in water metering functions. Transport time meters additionally use ultrasound like Doppler meters, however as an alternative of bouncing the sound waves off particles within the water like Doppler move meters, they ship ultrasound waves between two sensors separated from one another by a sure distance along the size of the pipe and makes use of the transmission time of the sound waves to calculate the rate of the water move. Because the velocity of sound in the water is thought, the speed of the water may be calculated primarily based on the offset in ultrasonic wave transmission time that happens because of the velocity of the water.
Transmission time meters could be costly relative to Doppler circulate meters as a outcome of many sensors and complex set up involved. They can be extra accurate because of the capacity to split the flow into horizontal cross sections and measure the rate of every part.
Flow unit measurement strategies in full tube applications
Venturi meters
Venturi circulate meters use the Venturi effect to measure flow in a full or pressurized pipe through the use of the converging section of the pipe to limit the circulate. According to the continuity equation, the cross-sectional area of the converging part is small and subsequently the velocity is greater within the throat. Due to vitality conservation and Bernoulli’s precept, greater velocities within the throat lead to a drop in throat pressure. The move price can then be determined by measuring the pressure drop within the convergent section and calculating the move price utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering purposes as a end result of the pressure measurement ports can become clogged in wastewater purposes.
Magnetic flowmeter
The electromagnetic flow meter works by applying a magnetic field to the fluid passing by way of the pipe. This causes a small electron potential distinction that may be measured by the electrode sensor (due to Faraday’s regulation and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the speed of the water, and the continuity equation can then be used to calculate the move price.
An advantage of the magnetometer is that the metering part is similar diameter as the adjoining pipe, so the magnetometer causes no additional head loss. For the most part, magnetometers are used for full (pressure) pipe purposes, however nowadays open channel magnetometers can be used.
Turbine flowmeter
A turbine move meter is a mechanical move meter that makes use of a rotating turbine in circulate to measure the circulate of water in a pipe. The speed of the turbine is proportional to the velocity and the circulate price can then be calculated utilizing the continuity equation. Turbine flow meters are only used for water functions because of potential issues with wastewater solids assortment and clogging generators.
Conclusion
There are some ways to measure flow. Each method has totally different advantages, disadvantages and accuracy in numerous functions.
It is necessary to grasp the traits of various flow measurement techniques to help choose the right kind of flow metering on your utility or to correctly interpret the flow measurements of current circulate meters. Tools like Apure (IoT-based water knowledge analysis) help to look at measurements collected by move meters and perform diagnostics to know flow meter performance and rapidly course of and analyze the information. Contact us for technical or product service help.
More articles on move meters:
Mass move rate vs volumetric flow rate
Relation between circulate and stress
Ultrasonic circulate meter working precept
Difference between move meter and circulate transmitter
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Table of Contents
What is flow units?
Continuity of move equation
Common flow unit metering methods in open channels
Eyeball methodology
Flow depth (Manning)
Main equipment
Surface Velocity Meters
Transport time meters
Flow unit measurement strategies in full tube applications
Venturi meters
Magnetic flowmeter
Turbine flowmeter
Conclusion
What is move units?
Flow fee is the quantity of fluid that passes via a unit of time. In water resources, flow is commonly measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a selection of different units. The measurement of water useful resource circulate is necessary for applications such as system control, billing, design and lots of other purposes. There are a number of ways to measure move in a water useful resource system. This article outlines some of the more widespread methods of flow measurement and provides some helpful information about move units measurement.
Continuity of move equation
For water flowing in a pipe beneath steady-state circumstances (i.e., not various with time), continuity means that water flowing into one finish of the pipe must move out of the opposite end. This additionally means that the circulate within the pipe is similar at any point alongside the length of the pipe. The continuity equation can be expressed as
Flow = Velocity * Area
The concept of continuity in steady state circumstances results in the product of velocity * space being equal to a continuing at any level in the pipe. This is a helpful precept for making circulate measurements, as proven below.
This is an example of using the continuity equation to calculate move. Velocity is measured at 10 toes per second and the cross-sectional area of the circulate is measured at 10 square feet. Flow price = 10 feet per second * 10 sq. toes = 100 cubic ft per second.
Common move unit metering strategies in open channels
Eyeball methodology
It is usually helpful to estimate the move velocity and cross-sectional area by eye after which multiply the move velocity by the area to acquire the circulate velocity (continuity equation). A ruler or tape measure can be utilized to improve the accuracy of cross-sectional area measurements, and a stopwatch can be used to improve velocity measurements by timing floating debris shifting a set distance. The eyeball methodology can be utilized to estimate move when only an “order of magnitude” of move is required or when the circulate fee is simply too low to be measured with a circulate meter.
Flow depth (Manning)
When the channel cross-sectional area and channel slope are identified and uniform circulate conditions exist, the Manning’s equation can be used to calculate circulate by measuring depth only. The Manning’s equation is an empirical equation that describes the relationship between move rate in an open channel underneath uniform flow situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate signifies that depth doesn’t differ with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t relevant to steadily altering move situations, corresponding to backwater circumstances upstream of a dam or weir.
The depth circulate methodology of circulate measurement is more accurate than the “eyeball” method. The major challenge with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform flow conditions. This method is often used with ultrasonic flow meters to estimate the move of a river by measuring only the water stage of the river. Often in these causes, the river level/flow relationship is developed with the help of complicated river hydraulic fashions to account for complex channel geometry and channel friction conditions.
Main gear
The main gadget is used to measure move in open channels, utilizing structures similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be transformed to a move fee utilizing an equation or rated curve equation.
Primary devices work by forcing the move through a path of important depth, for example on the prime of a weir or on the throat of a flume. In technical phrases, the critical depth is defined as the depth of the minimum particular power state that ends in a particular discharge. In apply, this minimal state of vitality implies that just one move corresponds to the important depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is therefore called a “primary” system.
Primary gadgets are a really handy method of move measurement as a end result of the depth may be measured from above the flow with out the want to insert a sensor in the water. This makes major flow meters extra dependable and easier to take care of. A disadvantage of main gadgets is that they’ll trigger head loss and backwater within the system. Primary devices are often thought of to be probably the most correct technique of measuring open channel flow.
Surface Velocity Meters
An space velocity meter is an open channel move meter that measures move by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional space utilizing the geometry of the pipe or channel. The flow fee is then calculated by multiplying the move area by the rate using the continuity equation, hence the identify “AV meter”. Velocity is often measured utilizing a Doppler sensor, which displays ultrasound waves again from particles within the fluid and makes use of the Doppler shift in the reflected sound sign to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.
AV meters are often used to measure open channel circulate in sewers because the probes are relatively small and they are often installed in current sewer pipes without causing important head loss within the pipe. This also permits them to be used for short-term or short-term circulate metering applications for sewer research. one drawback of AV meters is that the sensor should be installed within the fluid. In sewers, this requires frequent upkeep to wash the sensor. AV meters are sometimes thought-about less accurate than major move meters because main devices only need to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters
Transport time meters were developed within the oil trade to precisely measure move in giant pipelines. They have been used with some success for open channel move in water metering purposes. Transport time meters also use ultrasound like Doppler meters, however as an alternative of bouncing the sound waves off particles within the water like Doppler flow meters, they ship ultrasound waves between two sensors separated from each other by a certain distance along the length of the pipe and makes use of the transmission time of the sound waves to calculate the rate of the water flow. Because the velocity of sound within the water is thought, the speed of the water may be calculated based mostly on the offset in ultrasonic wave transmission time that happens because of the velocity of the water.
Transmission time meters may be expensive relative to Doppler move meters due to the many sensors and complicated installation concerned. They can be more accurate because of the ability to separate the circulate into horizontal cross sections and measure the velocity of every section.
Flow unit measurement methods in full tube functions
Venturi meters
Venturi move meters use the Venturi impact to measure move in a full or pressurized pipe by utilizing the converging section of the pipe to limit the flow. According to the continuity equation, the cross-sectional area of the converging section is small and therefore the speed is greater in the throat. Due to power conservation and Bernoulli’s principle, larger velocities in the throat lead to a drop in throat stress. The flow rate can then be determined by measuring the pressure drop within the convergent part and calculating the move fee utilizing Bernoulli’s equation. Venturi meters are more frequent in water metering functions as a result of the strain measurement ports can turn into clogged in wastewater applications.
Magnetic flowmeter
The electromagnetic circulate meter works by applying a magnetic subject to the fluid passing through the pipe. This causes a small electron potential distinction that might be measured by the electrode sensor (due to Faraday’s regulation and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the rate of the water, and the continuity equation can then be used to calculate the flow fee.
An benefit of the magnetometer is that the metering section is the same diameter because the adjacent pipe, so the magnetometer causes no additional head loss. For essentially the most part, magnetometers are used for full (pressure) pipe functions, however these days open channel magnetometers can be used.
Turbine flowmeter
A turbine circulate meter is a mechanical move meter that makes use of a rotating turbine in flow to measure the circulate of water in a pipe. The pace of the turbine is proportional to the velocity and the circulate price can then be calculated utilizing the continuity equation. Turbine circulate meters are only used for water purposes due to potential issues with wastewater solids assortment and clogging turbines.
Conclusion
There are some ways to measure circulate. Each methodology has totally different advantages, disadvantages and accuracy in several functions.
It is necessary to grasp the characteristics of various flow measurement techniques to assist choose the best sort of circulate metering on your utility or to correctly interpret the flow measurements of current flow meters. Tools like Apure (IoT-based water information analysis) help to look at measurements collected by flow meters and perform diagnostics to grasp circulate meter performance and quickly course of and analyze the data. Contact us for technical or product service assist.
More articles on circulate meters:
Mass flow rate vs volumetric circulate price
Relation between move and pressure
Ultrasonic move meter working precept
Difference between flow meter and circulate transmitter